1. Field of the Invention
The present invention relates to a process for selectively ortho-methylating a cyclohexanone having at least one ortho-hydrogen in the vapor phase, and more particularly to a methylation process of cyclohexanone for producing 2-methylcyclohexanone, 2,6-dimethylcyclohexanone and 2,6-xylenol.
2. Description of the Prior Art
2-methylcyclohexanone and 2,6-dimethylcyclohexanone are useful in chemical applications as intermediates. 2,6-xylenol is frequently used as a precursor to 2,3,6-trimethylphenol and other useful products. 2,6,-xylenol also finds uses in polymer and plastics applications such as that described in U.S. Pat. Nos. 3,446,856 and 3,994,982.
Currently, a process for the synthesis of 2,6-xylenol, which involves the vapor phase reaction of phenol with methanol in the presence of an acidic solid catalyst such as alumina, is in industrial use. However, in this process, the selectivity in the site of alkylation is only limited. That is, not only the ortho-positions of the phenolic nucleus but also the meta and para-positions thereof are subject to alkylation, so that a complicated procedure for the separation and purification of desired reaction products is required.
Another industrial process for the ortho-alkylation of phenol is based on the vapor phase reaction in the presence of magnesium oxide catalyst. However, this catalyst requires high temperature of 475.degree. C. or higher, practically 500.degree. C. or higher to achieve sufficient reaction. Moreover, its activity tends to become lower after a short period time of reaction.
In order to solve these problems, there have been proposed a number of catalysts including, for example, combinations of magnesium oxide and other oxides, combinations of iron oxide and other oxides, and the like. However, owing to the effect of the delocalized .pi. electronic cloud of the benzene ring in phenol, these catalysts still have the disadvantages that they are insufficient in selectivity for ortho-alkylation and the service life of them are not desirably long. In addition, many undesirable by-products such as 2,4,6-trialkylphenol are formed.